An AC/DC converter is designed to convert an alternating current (“AC”) mains voltage to a regulated direct current (“DC”) output voltage to power an electronic load such as a tablet, printer, modem, cell phone, or personal computer. In many applications, an AC/DC converter is required to operate with a wide input-output voltage range. For example, electricity supply voltage varies in different countries. China has a supply voltage between 220 v and 230 v, and the U.S. supply voltage is between 110 v and 130 v. A laptop that can work in both countries needs to have a universal AC/DC adapter that is able to operate with the supply voltage ranges of both countries. Further, as new technologies and applications emerge, such as the quick charge (QC) 2.0 of Qualcomm and USB Type C connectors, an AC/DC converter may be required to operate with a wide output voltage range. It is well understood, however, conversion efficiency of an AC/DC converter drops significantly when regulating an output voltage at very wide input and output voltage ranges. Further, an AC/DC converter usually operates at a low switching frequency, and the power density is also low. An AC/DC converter that can operate with wide input and output voltage ranges without suffering from reduced efficiency and low power density is desired.